The invention applies to the field of medical imaging, and more particularly the field of positron emission tomography (PET).
Today, physicians use medical imaging to establish a diagnosis, in oncology, for example, or as therapeutic treatment in radiotherapy. The imaging devices, for example X scanner (CT for Computed Tomography), magnetic resonance (MRI) or PET, produce images supplying anatomical or functional information. The images undergo image processing algorithms so as to help the physician in establishing his diagnosis. One image processing consists of a segmentation operation aiming to group together pixels of the image according to predefined criteria. The pixels are thus grouped together in regions that constitute a partition of the image, for example to visualize the organs or particular structures such as tumors.
Document FR-0505441 describes a method for segmenting a three-dimensional image or sequence of images comprising, in the performance order of the method, the following steps:                dividing the image or sequence of images into a plurality of regions; then        hierarchically linking the regions resulting from the division so as to obtain the image or sequence of three-dimensional images partitioned into regions of interest.        
However, this segmentation method is not effective enough to segment small structures such as tumors. In fact, the radioactive concentration of the tracer is underestimated inside these small structures. This effect is commonly called the partial volume effect and is the consequence of the limited spatial resolution and the chosen sampling.